1. Field of the Invention
The present invention relates to a system of testing a liquid crystal display device, and more particularly, to a system and method for testing the quality of a liquid crystal display device.
2. Discussion of the Related Art
With the development of various portable electric devices such as mobile phones, personal digital assistants (PDA), and notebook computers the need for small, light weight and power efficient flat panel display devices for such portable devices has correspondingly increased. Flat panel display device technologies such as liquid crystal display (LCD) technology, plasma display panel (PDP) technology, field emission display (FED) technology, and vacuum fluorescent display (VFD) technology have been actively researched to fill this need. Of these flat panel display devices, the LCD has the advantages of being manufactured using current mass production techniques, and having efficient driving schemes and superior image quality.
An LCD is a device for displaying information on a screen using refractive anisotropy of liquid crystal. As shown in FIG. 1, a typical LCD 1 comprises a lower substrate 5, an upper substrate 3, and a liquid crystal layer 7 formed between the lower substrate 5 and the upper substrate 3. The lower substrate 5 is a driving device array substrate. A plurality of pixels (not shown) is formed on the lower substrate 5, and a driving device such as a thin film transistor (TFT) is formed at each pixel. The upper substrate 3 is a color filter substrate, and a color filter layer for reproducing real color is formed thereon. Further, a pixel electrode and a common electrode are formed on the lower substrate 5 and the upper substrate 3, respectively. An alignment layer is formed on the lower substrate 5 and the upper substrate 3 to align liquid crystal molecules of the liquid crystal layer 7 uniformly.
The lower substrate 5 and the upper substrate 3 are bonded together using a sealing material 9, and the liquid crystal layer 7 is formed therebetween. In operation the liquid crystal molecules of the liquid crystal layer 7 are reoriented by the driving devices formed on the lower substrate 5 to control the amount of light transmitted through the liquid crystal layer to thereby display information.
Fabrication processes for a LCD device can be divided into a driving device array substrate process for forming driving devices on the lower substrate 5, a color filter substrate process for forming the color filter on the upper substrate 3, and a cell process. These processes will be described with reference to FIG. 2 as follows.
The driving device array process includes forming a plurality of gate lines and data lines are on the lower substrate 5 to define pixel areas; forming a thin film transistor connected to both a gate line and a data line at each pixel area (S101); and forming pixel electrodes connected to each thin film transistor to drive the liquid crystal layer according to a signal applied through the thin film transistor.
In the color filter process (S104) R (Red), G (Green), and B (Blue) color filter layers for reproducing the color and a common electrode are formed on the upper substrate 3.
Alignment layers are formed on the lower substrate 5 and the upper substrate 3, respectively, and each alignment layer is rubbed to provide an initial alignment (that is, a pretilt angle and alignment direction) to the liquid crystal molecules of the liquid crystal layer between the lower substrate 5 and the upper substrate 3 through surface anchoring (S102 and S105). Spacers for maintaining the cell gap constant and uniform are dispersed on the lower substrate 5, and the sealing material 9 is applied on a peripheral portion of the upper substrate 3 to bond the lower substrate 5 to the upper substrate 3 under pressure (S103, S106, and S107).
The lower substrate 5 and the upper substrate 3 are made from large glass substrates. The large glass substrates includes a plurality of unit panel areas on which the driving devices such as TFTs and the color filter layer are formed. To fabricate individual liquid crystal unit panels, the assembled glass substrate is cut into unit panels (S 108). Liquid crystal may be injected into the individual liquid crystal unit panel through a liquid crystal injection opening (S109). The filled liquid crystal unit panel is completed by sealing the liquid crystal injection opening. Each sealed liquid crystal unit panel is tested (S110).
In an injection method of the related art for filling liquid crystal unit panels a pressure difference is used to induce the injection of liquid crystal through the liquid crystal injection opening. FIG. 3 shows a device of the related art for injecting the liquid crystal into the liquid crystal panel. As shown in FIG. 3, a container 12 holding the liquid crystal is placed in a vacuum chamber 10. The liquid crystal panel is positioned in an upper portion of the container 12. The vacuum chamber 10 is connected to a vacuum pump used to maintain a vacuum within the vacuum chamber 10. A liquid crystal panel transferring device (not shown) is installed in the vacuum chamber 10 to move the liquid crystal panel into the container 12 to bring the injection opening 16 of the liquid crystal panel 1 into contact with the surface of the liquid crystal 14 (this step is called a liquid crystal dipping injection step).
However, there are problems associated with forming a liquid crystal layer using the injection method of the related art.
First, considerable time is used to inject the liquid crystal into the panel 1. The thickness of the gap between the driving device array substrate and the color filter substrate in the liquid crystal panel may be on the order of magnitude of micrometers, and therefore a very small amount of liquid crystal may be injected into the liquid crystal panel per unit time. For example, it may take about 8 hours to completely inject liquid crystal into a 15-inch liquid crystal panel 1. Thus, the use of the liquid crystal injection method results in increased time to complete the liquid crystal fabrication process, thereby reducing fabricating efficiency.
Secondly, use of the liquid crystal injection method increases the consumption of liquid crystal. A small amount of liquid crystal of the liquid crystal contained in the container 12 is injected into the liquid crystal panel 1. However, when the liquid crystal is exposed to the atmosphere or to a certain gases, the liquid crystal is contaminated by reaction with the gases or atmosphere and by the impurities introduced through contact with the liquid crystal panel 1. Therefore, the remaining liquid crystal in the container 12 is discarded after liquid crystal is injected into a plurality of liquid crystal panels 1, thereby increasing the cost associated with liquid crystal panel fabrication.